New answers tagged

3

Even if we ignore the salaries of everyone involved; engineers, sales people, management, Q/A teams, manufacturing teams, more sales people, and then a few spare engineers... I don't understand. If it's just designing a jet engine, then raw materials cannot possibly be a major factor even if it's something like titanium or composites. While the raw ...


0

To my eye, comparing with memory of many YouTube videos, the conical ends of the combustion chamber are too short and the bends in the exhaust pipe are both too small radius and the pipe is slightly flattened at those bends. The angle of the exhaust pipe shouldn't matter -- I've seen these build completely straight and gotten to run -- but the sharp bends ...


2

The key to the operation of a valveless pulse jet is the oscillating shock wave created by repeated explosions in the combustion chamber. In this video they talk about using a spark plug to trigger these explosions initially, and once the engine is running the process is self sustaining. Looking at your video I don't see any connections to the engine except ...


2

The jet engine efficiency is unfortunately more complicated than just a one-to-one function between static Turbine Inlet Temperature and efficiency. Thermodynamic efficiency of a turbine engine is defined as the useful generated power extracted from the chemical energy added by the fuel. The following is extracted from a paper format uni book on aircraft ...


2

You'll have a hard time finding an exact answer, as that's unlikely to be public information, but here are some general trends: In the case of the high pressure turbine, the blades are one of the key company jewels. These are one of the highest technology pieces of the engine, and contributes a large part of the competitive advantage of one engine over ...


1

The easiest way to understand this is by comparison to a piston 4 cycle engine: In the piston engine the 4 cycles occur in the same location, but at different times. I.e. the combustion cycle gives way to the exhaust cycle as the fuel is burned up and pushed out the exhaust valve. On each subsequent cycle the fuel air mixture must be ignited again. ...


10

The autoignition temperature of kerosene is 428F. The temperature coming out of the last stage is usually above that at moderate power settings, up to 7-800 F or more at takeoff thrust. However the temperature has dropped somewhat by the time the air gets to the fuel nozzle, and in heavy rain there may be superheated water cooling things down some more, ...


19

Jet fuel will not self-ignite when starting a modern turbine engine. This article from the WingMag Aviation Magazine says: As the temperature isn’t quite sufficient to initiate self-ignition (the autoignition temperature of aviation fuel is around 220 degrees Celsius), spark plugs are arranged around the combustion chamber. They generate a spark that ...


4

those are to help the fuel ignite during a cold start, when all the components in the hot section are at ambient temperature and there exist no flames in the burner cans. And as pointed out by Jan Hudec, the start motor (if the engine has one) or the APU (if it does not) cannot spin the compressor fast enough to heat the air to the point where the injected ...


1

To keep it simple (source for all that follows is Wikipedia - Propfan): You can think of the contemporary propfan as a turboprop that has two high rpm contra-rotating propellers or fans with six or more highly swept fan blades each. These fans are driven by a turbine engine through a reduction gear or a low-speed free turbine. High rpm is used to reach ...


3

That's one badly-worded quote: Single spool jet engine. These are those jet engines who have one shaft inside them. The compressors and turbines rotate on a same shaft. Correct. In a single-spool engine, all of the compressor and turbine stages rotate at the same speed because they're attached rigidly to the shaft. The speed of compressors and ...


-1

Your question answers itself. If they have a single shaft and no gear box, then they rotate at the same speed. If there is a gearbox then that gearbox gives you the speed difference.


0

So this article, says that the average brand new CFM56-7 will go 18,000 cycles (i.e. flights) before its first shop visit. You can't replace the turbine blade on-wing, only in the overhaul shop. So we could say that the blades would last at least 18,000 flights, potentially longer.


1

I could be wrong but reverse thrust from the running engine helped to stop the plane1 as it was approaching at a great speed way over the recommended landing speed, so shutting the running engine off right at approach would have made the plane to overshoot the runway, making the situation worse. 1: Source: [...] The aircraft then rolled left seven ...


0

Ground idle and in-fight idle are different. In-flight idle would move aircraft on the ground and would require a bit of brakes to keep the aircraft stationary. Additionally, landing roll would be longer. Therefore, ground idle activates on most jet aircrafts after touchdown. This activation is usually occurs after a small delay, taking into account that ...


2

For one there is less resistance to the fan and compressor due to the decreased air density -> more rpm out of the given power. On the other hand, the mass flow needs to be high enough to sustain the operation of the engine -> both lead to a higher rpm...


0

Both, and it depends. When a Hot Section Inspection is done, they are looking for mostly blade erosion beyond dimensional limits, and cracks. Some cracks are allowed if the OEM's engineering determines they are benign (sometimes cracks form which fully relieve the stress that initiated them and the crack stops propagating - such cracks can be left alone, ...


6

Because most people are right handed. Let me expand a bit on that: Ancient Boats Our story begins in ancient times, long before aviation took off. Early boats were steered with a steering oar attached to the side of the boat. You can see one in the following tapestry: (image source: Wikimedia) Since most people are right handed, the steering oar was ...


8

@Michael Hall said it best, in the first sentence of item 1 of his answer: There are simply too many variables for a definitive answer. Here are two extremes to illustrate the range of answers insofar as altitude is concerned: Let's say you have a 747 at it's optimum altitude in cruise with all four engines operating, say 37,000 just for the heck of it. ...


0

There are simply too many variables for a definitive answer. It depends greatly upon weight, how high the mountains are, starting altitude, and distance available to climb. 1800 feet seems much lower than necessary. Under normal conditions in an unpressurized aircraft with passengers you would want to get below 10,000 feet. However, in an emergency where ...


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